JP2017175207A - Base station, radio communication system, and calibration method of radio communication system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve accuracy of calibration in a radio transmission/reception circuit between a plurality of transmission/reception points.SOLUTION: In one aspect, a base station 101 connected with a plurality of transmission/reception points 102 comprises a calibrator 404. The calibrator 404 calculates a calibration coefficient to be multiplied by weights of beam forming communication of the respective transmission/reception points 102 on the basis of beam forming communication of each of the transmission/reception points 102.SELECTED DRAWING: Figure 4

Description

  The present disclosure relates to a base station, a wireless communication system, and a calibration method.

  In mobile radio communication, the channel state (radio characteristics) of a radio channel between a base station and a radio terminal changes with time and also changes with frequency. For this reason, estimation of channel states of the downlink radio channel from the base station to the radio terminal and the uplink radio channel from the radio terminal to the base station is performed.

  When the base station and the radio terminal communicate by time division multiplexing, it can be estimated that the channel states of the uplink radio channel and the downlink radio channel are equivalent.

  However, what can be estimated as equivalent is the channel state of the air channel in the air between the antenna of the base station and the antenna of the wireless terminal. On the other hand, the radio channel estimated by the base station and the radio terminal includes the response characteristic (transfer function) of the radio transmission / reception circuit between the channel estimation unit and the antenna. The channel state with the channel may not be estimated to be equivalent. Therefore, calibration of the radio transmission / reception circuit is performed so that it can be estimated to be equivalent.

JP 2013-534380 A International Publication No. 2011/155360 JP 2011-199850 A JP 2013-509082 A

Kentaro Nishimori, Keizo Nagamori, Yasushi Takatori, Toshikazu Hori, “Examination of real-time correction method of adaptive array for TDD system”, A.P99-3, IEICE Tech. 17-22, April 1999 Yasuyoshi Noda, Yoshitaka Hara, Yasuhiro Yano, Hiroshi Kubo, “Antenna self-calibration using bidirectional channel measurement in TDD system”, RCS2008 / 12, IEICE Tech. 69-74, May 2008 H. Fukuzono, et al, "Weighted-combining calibration for implicit feedback beamforming on downlink multiuser MIMO systems," PIMRC 2013, Jun. 2013. F. Huang, Y. Wang, J. Geng, D. Yang, "Antenna mismatch and calibration problem in coordinated multi-point transmission system," IET Commun, 2012, Vol. 6, Iss 3, pp. 289-299.

  When a base station is connected to a plurality of transmission / reception points and the plurality of transmission / reception points cooperate with each other to communicate with a radio terminal, it is preferable that radio signals received by the radio terminal from the plurality of transmission / reception points are the same. Therefore, it is necessary to accurately calibrate the base station connected to the plurality of transmission / reception points.

  In view of the above, one of the purposes of the disclosure is to improve the accuracy of calibration of a base station connected to a plurality of transmission / reception points.

  In one aspect, a base station connected to a plurality of transmission / reception points includes a calibrator. The calibrator calculates a calibration coefficient for correcting the weight of the beam forming communication at each of the plurality of transmission / reception points based on the beam forming communication at each of the plurality of transmission / reception points.

1 is an overall view of a wireless communication system according to Embodiment 1. FIG. (A) is a figure which shows an example in which a radio signal is transmitted from a transmission / reception point to a wireless terminal through a DL (Down Link) wireless channel, and (B) is wireless from the wireless terminal to the transmission / reception point through a UL (Up Link) wireless channel. It is a figure which shows an example in which a signal is transmitted. 2 is a functional block diagram of a base station, a transmission / reception point, and a wireless terminal of the wireless communication system according to Embodiment 1. FIG. 2 is a functional block diagram of a base station, a transmission / reception point, and a wireless terminal of the wireless communication system according to Embodiment 1. FIG. 3 is a flowchart of calibration processing of the wireless communication system according to the first embodiment. 6 is a diagram for describing self-calibration processing of the wireless communication system according to the first embodiment. FIG. (A) is a figure explaining the self-calibration process of the radio | wireless communications system which concerns on Embodiment 1, (B) is a figure explaining the self-calibration process of the radio | wireless communications system which concerns on Embodiment 1. FIG. FIG. 3 is a sequence diagram of calibration processing of the wireless communication system according to the first embodiment. FIG. 3 is a diagram for explaining calibration of the wireless communication system according to the first embodiment. FIG. 3 is a diagram for explaining calibration of the wireless communication system according to the first embodiment. 3 is another overall view of the wireless communication system according to Embodiment 1. FIG. 3 is an overall view of a wireless communication system according to Embodiment 2. FIG. 6 is a functional block diagram of a wireless communication system according to Embodiment 2. FIG. 10 is a flowchart of calibration processing according to the second embodiment. FIG. 10 is a sequence diagram of calibration processing according to the second embodiment. FIG. 10 is a sequence diagram of calibration processing according to the third embodiment. (A) is a hardware block diagram of a base station and a transmission / reception point, and (B) is a hardware block diagram of a wireless terminal.

  The disclosure will be described below. In addition, the same code | symbol is attached | subjected and demonstrated to the component of the same name. Further, when a plurality of the same kind appears in one drawing, they are distinguished by attaching # 1, # 2,.

(Embodiment 1)
FIG. 1 is an overall view of a communication system according to the first embodiment. The wireless communication system 100 includes a base station 101, transmission / reception points 102 # 1 and 102 # 2, and a wireless terminal 103.

  Transmission / reception points 102 # 1 and 102 # 2 are connected to the base station 101. For connection between the base station 101 and the transmission / reception points 102 # 1 and 102 # 2, for example, one or more of wired communication using an optical fiber and wireless communication using a microwave line is used. Each of the transmission / reception points 102 # 1 and 102 # 2 forms a wireless area.

  When the wireless terminal 103 is located in the wireless area, the wireless terminal 103 can communicate with a transmission / reception point that forms the wireless area. In FIG. 1, the wireless terminal 103 and the transmission / reception points 102 # 1 and 102 # 2 can communicate with each other. Therefore, the transmission / reception points 102 # 1 and 102 # 2 can communicate with the wireless terminal 103 in cooperation. Note that when the wireless terminal 103 can communicate with the transmission / reception points 102 # 1 and 102 # 2, the wireless terminal 103 is located in the base station 101.

  Base station 101 is also connected to the core network, and relays communication between the core network and transmission / reception points 102 # 1 and 102 # 2.

  In many wireless communication systems, the base station 101 performs baseband signal processing, and the transmission / reception points 102 # 1 and 102 # 2 perform conversion processing between the baseband signal and the wireless signal and processing of the wireless signal. In other words, when base station 101 generates a baseband signal and transmits the generated baseband signal to transmission / reception points 102 # 1 and 102 # 2, transmission / reception points 102 # 1 and 102 # 2 are converted into radio signals. To transmit a wireless signal to the wireless terminal 103. When the transmission / reception points 102 # 1 and 102 # 2 receive a radio signal from the radio terminal 103, the transmission / reception points 102 # 1 and 102 # 2 convert the baseband signal into a baseband signal, and transmit the converted baseband signal to the base station 101. Perform the following process.

  The wireless terminal 103 is a device that performs wireless communication with transmission / reception points forming a wireless area. As described above, in FIG. 1, the wireless terminal 103 can perform wireless communication with the transmission / reception points 102 # 1 and 102 # 2.

  The base station 101 may be referred to variously such as a BBU (Base Band Unit), a C-BBU (Centralized Base Band Unit), a baseband station, or a control station. The transmission / reception points 102 # 1 and 102 # 2 may be referred to variously, such as RRH (Remote Radio Head) or TP (Transmission Point). The base station 101 and the transmission / reception points 102 # 1 and 102 # 2 may be collectively referred to as Node B (Node B, NB) or evolved Node B (eNode B). In addition, the wireless terminal 103 can be referred to variously such as a user equipment (UE), a mobile station (MS), a user terminal, or a subscriber station.

  2A and 2B illustrate an example of communication between the transmission / reception point 102 and the wireless terminal 103. FIG. In FIG. 2A, a radio signal is transmitted from the transmission / reception point 102 to the radio terminal 103 through a DL (downlink) radio channel. In FIG. 2B, a radio signal is transmitted from the radio terminal 103 to the transmission / reception point 102 through the UL (uplink) radio channel.

  Assume that the transmission / reception point 102 and the wireless terminal 103 perform time division duplex (TDD) communication. In this case, since the transmission / reception point 102 and the radio terminal 103 communicate using the same frequency, the DL radio channel and the UL radio channel can be regarded as the same. Therefore, the radio characteristics of the DL radio channel and the UL radio channel can be equated.

  Based on the same view, the base station 101 connected to the transmission / reception point 102 determines the channel of the detailed DL radio channel according to the radio characteristics (channel state) of the UL radio channel estimated using the UL reference signal from the radio terminal 103 or the like. The state can be estimated. Accordingly, the base station 101 connected to the transmission / reception point 102 can perform transmission / reception beam forming by multiplying the DL data signal by the weight. Also, the radio terminal 103 does not need to report the channel state of the downlink radio channel, and can reduce the overhead of the control signal.

  However, in reality, the estimation of the channel state of the radio channel is performed via the transmission / reception unit. For this reason, the channel state of the estimated radio channel is a channel state (channel state including the transmission unit and the reception unit) that is a combination of the channel state between antennas and the channel state of the transmission / reception unit.

  FIG. 3 is an example of a functional block diagram of the base station 101, the transmission / reception point 102, and the wireless terminal 103 of the wireless communication system 100.

  The transmission / reception point 102 includes a transmission unit 302 # 1, a reception unit 303 # 1, and a transmission unit 302 # 2 and a reception unit 303 # 2, corresponding to the antennas 304 # 1 and 304 # 2. In addition, the base station 101 includes a baseband unit 301. The wireless terminal 103 includes a transmission unit 311, a reception unit 312, and a baseband unit 301.

The response characteristics of the transmitting unit 302 # 1 and the receiving unit 303 # 1 to which the antenna 304 # 1 is connected are denoted as T ₁ and R ₁ respectively, and the transmitting unit 302 # 2 to which the antenna 304 # 2 is connected and The response characteristics of receiving section 303 # 2 are denoted as T ₂ and R ₂ , respectively. In other words, the response characteristic from the input of the baseband signal to the transmission unit 302 # 1 to the transmission of the radio signal by the antenna 304 # ₁ is denoted as T1. Similarly, a response characteristic from reception of a radio signal by the antenna 304 # 1 to output of a baseband signal from the reception unit 303 # ₁ is denoted as R1. The same applies to T ₂ and R ₂ .

The antenna 304 # 1 and the channel state of the radio channel between the antennas of the wireless terminal 103 is expressed as h _1, the channel condition of the wireless channel between the antennas of the antenna 304 # 2 and the radio terminal 103 h ₂ Is written. Further, the response characteristic of the transmission unit 311 of the wireless terminal 103 is denoted as t _1, and the response characteristic of the reception unit 312 is denoted as r ₁ .

Let f _DL ^{(1) be} a channel state estimated by the baseband unit 314 of the wireless terminal 103 from the input of the baseband signal to the transmission unit 302 # 1 to the output of the baseband signal of the reception unit 312. Also, let f _DL ^{(2) be} a channel state estimated by the baseband unit 314 of the wireless terminal 103, from the input of the baseband signal to the transmission unit 302 # 2 to the output of the baseband signal of the reception unit 312. At this time, f _DL ⁽¹⁾ and f _DL ⁽²⁾ are as follows.

^{_{f DL (1) = T 1}} × h 1 × r 1 ( Equation 1)
f _DL ⁽²⁾ = T ₂ × h ₂ × r ₁ (Formula 2)

Further, let f _UL ^{(1) be} the channel state from the input of the baseband signal to the transmission unit 311 to the output of the baseband signal of the reception unit 303 # 1 estimated by the baseband unit 301 of the base station 101. . Also, let f _UL ^{(2) be} the channel state estimated by the baseband unit 301 of the base station 101 from the input of the baseband signal to the transmission unit 311 to the output of the baseband signal of the reception unit 303 # 2. At this time, f _UL ⁽¹⁾ and f _UL ⁽²⁾ are as follows.

f _UL ⁽¹⁾ = t ₁ × h ₁ × R ₁ (Formula 3)
f _UL ⁽²⁾ = t ₁ × h ₂ × R ₂ (Formula 4)

Therefore, if any one of T ₁ ≠ R ₁ , T ₂ ≠ R ₂ , t ₁ ≠ r ₁ and t ₂ ≠ r ₂ holds, f _DL ⁽¹⁾ = f _UL ⁽¹⁾ and f _DL ^{( 2)} = f _UL ⁽²⁾ does not always hold. For this reason, the DL radio link channel and the UL radio link channel cannot be identified. Therefore, even if the channel state of the DL radio channel is estimated based on the estimation of the channel state of the UL radio channel, the estimation is not correct, precoding in the DL radio channel is not optimal, and communication characteristics deteriorate. .

  Therefore, it is necessary to perform calibration according to the response characteristics of the transmission unit 302 and the reception unit 303 of the transmission / reception point 102. In other words, it is necessary to use the calibration coefficient obtained by calibration to correct the precoder's precoding matrix or transmission / reception weight by the calibration coefficient, or to multiply the baseband signal by the calibration coefficient. is there.

  FIG. 4 is a detailed functional block diagram of the base station 101, the transmission / reception points 102 # 1 and 102 # 2, and the wireless terminal 103 of the wireless communication system 100 according to the present embodiment.

  As illustrated in FIG. 3, the wireless terminal 103 includes an antenna 313, a transmission unit 311, a reception unit 312, and a baseband unit 314. A radio signal received by the antenna 313 is output to the reception unit 312, converted into a baseband signal, and output to the baseband unit 314. Further, when the baseband signal is output from the baseband unit 314 to the transmission unit 311, it is converted into a radio signal and transmitted from the antenna 313. Further, the baseband unit 314 can perform channel estimation of the downlink radio channel.

  Each of the transmission / reception points 102 # 1 and 102 # 2 includes transmission units 302 # 1 and 302 # 2 and reception units 303 # 1 and 303 # 2. Each of transmitting sections 302 # 1 and 302 # 2 and receiving sections 303 # 1 and 303 # 2 is a radio circuit that performs conversion processing between a baseband signal and a radio signal and radio signal processing.

  The base station 101 includes baseband units 301 # 1 and 301 # 2, a core network interface 402, self-calibration units 403 # 1 and 403 # 2, and an RRH calibration unit 404. Each of baseband sections 301 # 1 and 301 # 2 includes precoders 401 # 1 and 401 # 2, respectively. Note that the RRH calibration unit 404 may be simply referred to as a calibrator.

  The core network interface 402 is an interface between the baseband units 301 # 1 and 301 # 2 and the core network. In other words, each of the baseband units 301 # 1 and 301 # 2 can communicate with the core network via the core network interface 402.

  The baseband unit 301 # 1 can input and output baseband signals to and from the transmission / reception point 102 # 1, and the baseband unit 314 of the wireless terminal 103 via the transmission / reception point 102 # 1, the reception unit 312 and the transmission unit 311. Can communicate with.

  The baseband unit 301 # 2 can input and output baseband signals to and from the transmission / reception point 102 # 2, and the baseband of the wireless terminal 103 is transmitted via the transmission / reception point 102 # 2, the reception unit 312 and the transmission unit 311. Communication with the unit 314 is possible.

  Self-calibration unit 403 # 1 is connected to transmission / reception point 102 # 1. The self-calibration unit 403 # 1 performs calibration of the transmission units 302 # 1 and 302 # 2 and the reception units 303 # 1 and 303 # 2 of the transmission / reception point 102 # 1. The self-calibration unit 403 # 2 is connected to the transmission / reception point 102 # 2. The self-calibration unit 403 # 2 performs calibration of the transmission units 302 # 1 and 302 # 2 and the reception units 303 # 1 and 303 # 2 of the transmission / reception point 102 # 2.

  Calibration by the self-calibration units 403 # 1 and 403 # 2 is referred to as self-calibration. The self-calibration coefficient obtained as a result of self-calibration is set in, for example, the precoder (beamformer) 401 of the baseband unit 301. The precoder 401 is a unit for multiplying a baseband signal input / output by the baseband unit by a weight and directing a beam in a predetermined direction. When the self-calibration coefficient is set in the precoder 401, the weight is corrected by multiplying the weight by the self-calibration coefficient. The calibration coefficient can be set at the transmission / reception point 102 in addition to being set in the precoder 401. By setting a calibration coefficient at the transmission / reception point 102, circuit constants and the like are corrected.

In self-calibration in the present embodiment, as shown in Non-Patent Document 2, the self-calibration coefficient u ₁ and the response characteristics T ₁ and T ₂ of the transmission unit 302 # 1 and the transmission unit 302 # ₂ , respectively. It is performed so as to multiply each of u ₂ . Each of the self-calibration coefficients u ₁ and u ₂ is determined so that the ratio between the above formula 1 and the above formula 3 is the same as the ratio between the above formula 2 and the formula 4. In other ^{_{words, u 1 × (f DL (}} 1) / f UL (1)) = u 2 × (f DL (2) / f DL (2)) to determine u ₁ and _{u 2} as is true . Using (Equation 1) to (Equation 4), the following equation is obtained.

u ₁ × (T ₁ × h ₁ × r ₁ ) / (t ₁ × h ₁ × R ₁ )
= U ₂ × (T ₂ × h ₂ × r ₁ ) / (t ₁ × h ₂ × R ₂ )

If the above equation holds, the channel characteristics in the range including the transmission unit and the reception unit become a constant multiple difference between the DL radio channel and the UL radio channel, and the channel characteristics of the DL radio channel and the UL radio channel are regarded as the same. can do. Organizing the above equations,

u ₁ × T ₁ / R ₁ = u ₂ × T ₂ / R ₂

Therefore, u ₂ / u ₁ = (T ₁ / R ₁ ) / (T ₂ / R ₂ ).

Each of the self-calibration units 403 # 1 and 403 # 2 outputs a self-calibration coefficient calculated from u ₁ and u ₂ to each of the precoders 401 # 1 and 402 # 2. Thereby, for example, when the precoders 401 # 1 and 402 # 2 perform precoding, this is the same as multiplying the baseband signal transmitted to the transmission unit 302 # 2 by the weight and further multiplying by u ₂ / u _1. .

In other words: Among the outputs of the precoder 401, when a signal output to the transmission unit 302 # 2 is expressed as So _{# 2} , correction is made so that (u ₂ / u ₁ ) × So _{# 2} is output to the transmission unit 302 # 2. Is done.

  A specific procedure for self-calibration will be described later.

  The inter-RRH calibration unit 404 performs calibration between the transmission / reception points 102 # 1 and 102 # 2 after the self-calibration of the transmission / reception points 102 # 1 and 102 # 2 is completed. This calibration is referred to as RRH calibration (or transmission / reception point calibration).

  The RRH calibration is performed by performing beam forming from each of the transmission / reception points 102 # 1 and 102 # 2 and transmitting / receiving a calibration signal to / from the wireless terminal 103. Since the self-calibration of each of the transmission / reception points 102 # 1 and 102 # 2 is completed before performing the RRH calibration, the beam forming can be performed more accurately than before the self-calibration. A predetermined reference signal can be used as the calibration signal.

  If accurate beamforming from the transmission / reception point 102 # 1 to the wireless terminal 103 is possible, the wireless signal from the antenna 304 # 1 and the wireless signal from the antenna 304 # 2 can be identified to the wireless terminal 103. For the baseband unit 301 # 1, the baseband signal from the receiving unit 303 # 1 and the baseband signal from the receiving unit 303 # 2 can be identified. The same is true for the transmission / reception point 102 # 2.

Therefore, when cooperative beamforming is performed from each of the transmission / reception points 102 # 1 and 102 # 2 after self-calibration, the inter-RRH calibration is performed in the same manner as the self-calibration.

c _{# 1} * ( _fDL ^{(# 1)} / _fUL ^{(# 1)} ) = c _{# 2} * ( _fDL ^{(# 2)} / _fUL ^{(# 2)} )

RRH calibration coefficients c _{# 1} and c _{# 2} may be determined so that

However, f _DL ^{(# 1)} is a channel state from the input of the baseband signal of the precoder 401 # 1 of the base station 101 to the output of the baseband signal of the reception unit 312 of the wireless terminal 103,

f _DL ^{(# 1)} = (W ₁ ^{(# 1)} × T ₁ ^{(# 1)} × h ₁ ^{(# 1)} + W ₂ ^{(# 1)} × T ₂ ^{(# 1)} × h ₂ ^{(# 1)} ) × r ₁ (Formula 5)

It can be. Here, T ₁ ^{(# 1)} and T ₂ ^{(# 1)} are response characteristics of the transmission units 302 # 1 and 302 # 2 of the transmission / reception point 102 # 1, and W ₁ ^{(# 1)} and W ₂ ^{(# 1)} is a weight corresponding to the antennas 304 # 1 and 304 # 2 of the transmission / reception point 102 # 1, and h ₁ ^{(# 1)} is an antenna 313 of the wireless terminal 103 from the antenna 304 # 1 of the transmission / reception point 102 # 1. H ₂ ^{(# 1)} is the channel state from the antenna 304 # 2 of the transmission / reception point 102 # 1 to the antenna 313 of the wireless terminal 103.

Similarly, f _UL ^{(# 1)} is a channel state from the input of the baseband signal of the transmission unit 311 of the wireless terminal 103 to the output of the baseband signal of the precoder 401 # 1 of the base station 101,

f _UL ^{(# 1)} = t ₁ × (h ₁ ^{(# 1)} × R ₁ ^{(# 1)} × W ₁ ^{(# 1)} + h ₂ ^{(# 1)} × R ₂ ^{(# 1)} × W ₂ ^{(# 1 ))} (equation 6)

It can be. Here, R ₁ ^{(# 1)} and R ₂ ^{(# 1)} are response characteristics of the receiving units 303 # 1 and 303 # 2 of the transmission / reception point 102 # 1.

Similarly, f _DL ^{(# 2)} is a channel state from the input of the baseband signal of the precoder 401 # 2 of the base station 101 to the output of the baseband signal of the reception unit 312 of the wireless terminal 103,

f _DL ^{(# 2)} = (W ₁ ^{(# 2)} × T ₁ ^{(# 2)} × h ₁ ^{(# 2)} + W ₂ ^{(# 2)} × T ₂ ^{(# 2)} × h ₂ ^{(# 2)} ) × r ₁ (Formula 7)

It can be. Here, T ₁ ^{(# 2)} and T ₂ ^{(# 2)} are response characteristics of the transmission units 302 # ₁ and 302 # 2 of the transmission / reception point 102 # 2, and W ₁ ^{(# 2)} and W ₂ ^{(# 2)} is a weight corresponding to the antennas 304 # 1 and 304 # 2 of the transmission / reception point 102 # 2, and h ₁ ^{(# 2)} is an antenna 313 of the wireless terminal 103 from the antenna 304 # 1 of the transmission / reception point 102 # 2. H ₂ ^{(# 2)} is the channel state from the antenna 304 # 2 of the transmission / reception point 102 # 2 to the antenna 313 of the wireless terminal 103.

Similarly, f _UL ^{(# 2)} is a channel state from the input of the baseband signal of the transmission unit 311 of the wireless terminal 103 to the output of the baseband signal of the precoder 401 # 2 of the base station 101,

f _UL ^{(# 2)} = t ₁ × (h ₁ ^{(# 2)} × R ₁ ^{(# 2)} × W ₁ ^{(# 2)} + h ₂ ^{(# 2)} × R ₂ ^{(# 2)} × W ₂ ^{(# 2 ))} (equation 8)

It can be. However, R ₁ ⁽²⁾ and R ₂ ^{(# 2)} are response characteristics of the receiving units 303 # 1 and 303 # 2 of the transmission / reception point 102 # 2.

Specifically, c _{# 2} and c _{# 1} are c _{# 2} / c _{# 1} = ( _fDL ^{(# 1)} / _fUL ^{(# 1)} ) / ( _fDL ^{(# 2)} / _fUL ^{(# 2)} It is decided so that it may become. It should be _noted that (Equation 5) to (Equation 8) are substituted into (f _DL ^{(# 1)} / f _UL ^{(# 1)} ) / (f _DL ^{(# 2)} / f _UL ^{(# 2)} ) to perform self-calibration. C _{# 2} / c _{# 1} is calculated as t ₁ , r ₁ , h ₁ ^{(# 1)} , h ₁ ^{(# 2)} , h ₂ ^{( # 1)} , h ₂ ^{(# 2)} , W ₁ ^{(# 1)} , W ₁ ^{(# 2)} , W ₂ ^{(# 1),} and W ₂ ^{(# 2)} .

For example, f _DL ^{(# 1)} / f _UL ^{(# 1)} is k ₁ × ((T ₁ ^{(# 1)} × T ₂ ^{(# 2)} ) / (R ₁ ^{(# 1} ) with respect to the constant k ₁ . ⁾ × R ₂ ^{(# 1)} )) × (r ₁ × t ₁ ) Further, f _DL ^{(# 2)} / f _UL ^{(# 2)} is k ₂ × ((T ₁ ^{(# 2)} × T ₂ ^{(# 2)} ) / (R ₁ ^{(# 2} ) with respect to the constant k ₂ . ⁾ × R ₂ ^{(# 2)} )) × (r ₁ × t ₁ ) Therefore, (f _DL ^{(# 1)} / f _UL ^{(# 1)} ) / (f _DL ^{(# 2)} / f _UL ^{(# 2)} ) is expressed as T ₁ ^{(# 1)} , T ₂ ^{(# 2)} , R ₁ ^{(# 1)} , R ₂ ^{(# 1)} , T ₁ ^{(# 2)} , T ₂ ^{(# 2)} , R ₁ ^{(# 2)} and R ₂ ^{(# 2)} .

For example, the inter-RRH calibration unit 404 corrects the weight used by the precoder 401 # 1 by 1 and corrects the weight used by the precoder 401 # 2 by c _{# 2} / c _{# 1.} # 1 and 401 # 2 are set. In other words, if the input to the precoder 401 # 2 is I, the precoding matrix is P, and the output from the precoder 401 # 2 is O, then O = (c _{# 2} / c _{# 1} ) × P × I. Like that.

  FIG. 5 is a flowchart for explaining the operation of the base station 101. In step S501, self-calibration of the transmission / reception points 102 # 1 and 102 # 2 is performed by the self-calibration units 403 # 1 and 403 # 2. The self-calibration of each transmission / reception point 102 # 1 and 102 # 2 may be performed in parallel or sequentially.

FIG. 6 shows one procedure of self-calibration by the self-calibration unit 403. First, as indicated by the one-dot chain line 601, a calibration signal is transmitted from the transmission unit 302 # 1, received by the reception unit 303 # 2, and T ₁ × H × R ₂ is calculated. Next, as indicated by the dotted line 602, a calibration signal is transmitted from the transmission unit 302 # 2, received by the reception unit 303 # 1, and T ₂ × H × R ₁ is calculated. H is the channel state between antennas 304 # 1 and 301 # 2. By dividing T ₁ × H × R ₂ by T ₂ × H × R ₁ , (T ₁ / R ₁ ) / (T ₂ / R ₂ ) is obtained.

  FIGS. 7A and 7B show another procedure of self-calibration by the self-calibration unit 403. FIG.

Referring to FIG. 7A, the self-calibration unit 403 transmits calibration signals to the wireless terminal 103 at different timings from the transmission unit 302 # 1 and the transmission unit 302 # 2, as indicated by dotted lines 701 and 702. Send. As indicated by the solid line 703, the wireless terminal 103 returns the estimation result of each channel state to the self-calibration unit 403. The estimation results of the respective channel states are T ₁ × h ₁ × r ₁ and T ₂ × h ₂ × r ₁ .

Next, referring to FIG. 7B, the wireless terminal 103 transmits a calibration signal to the transmission / reception point 102 as indicated by dotted lines 704 and 705. The self-calibration unit 403 receives the signals via the reception units 303 # 1 and 303 # 2, and the channel state is estimated. The estimation results of the respective channel states are t ₁ × h ₁ × R ₁ and t ₁ × h ₂ × R ₂ .

The self-calibration unit 403 calculates (T ₁ × r ₁ ) / (t ₁ × R ₁ ) by (T ₁ × h ₁ × r ₁ ) / (t ₁ × h ₁ × R ₁ ). Moreover, to calculate the _{(T 2 × h 2 × r} 1) / (t 1 × h 2 × R 2) by _{(T 2 × r 1) /} (t 1 × R 2). Next, ((T ₁ × r ₁ ) / (t ₁ × R ₁ )) / ((T ₂ × r ₁ ) / (t ₁ × R ₂ )) = (T ₁ / R ₁ ) / (T ₂ / R ₂ ).

Returning to the flowchart of FIG. In step S <b> 502, the RRH calibration unit 404 performs transmission beamforming from the transmission / reception point 102 # 1 and transmits a calibration signal to the wireless terminal 103. In step S503, the RRH calibration unit 404 performs reception beamforming at the transmission / reception point 102 # 1, and receives a calibration signal from the wireless terminal 103. Note that the baseband signal is multiplied by the same weight in transmission beamforming and reception beamforming. In step S502, f _DL ⁽¹⁾ is obtained as a result of DL channel estimation by the wireless terminal 103. In step S503, the baseband unit 301 # 1 obtains f _UL ⁽¹⁾ as a result of UL channel estimation.

In step S504, the RRH calibration unit 404 performs transmission beamforming from the transmission / reception point 102 # 2, and transmits a calibration signal to the wireless terminal 103. In step S505, the RRH calibration unit 404 performs reception beamforming at the transmission / reception point 102 # 2, and receives a calibration signal from the wireless terminal 103. As in steps S502 and S503, the baseband signal is multiplied by the same weight in transmission beamforming and reception beamforming. In step S504, f _DL ⁽²⁾ is obtained as a result of DL channel estimation by the wireless terminal 103. In step S505, the baseband unit 301 # 2 obtains f _UL ⁽²⁾ as a result of UL channel estimation.

In step S <b> 506, the RRH calibration unit 404 receives f _DL ⁽¹⁾ and f _DL ⁽²⁾ from the wireless terminal 103. In step S507, the RRH calibration unit 404 calculates an RRH calibration coefficient.

Note that the processing from S502 to S505 does not have to be executed in the order described in FIG. 5, and may be executed in any order. In step S506, the RRH calibration unit 404 receives f _DL ⁽¹⁾ and f _DL ⁽²⁾ from the wireless terminal 103, but is not limited to this. For example, the inter-RRH calibration unit 404 receives f _DL ⁽¹⁾ from the wireless terminal 103 after the process of step S502, and the inter-RRH calibration unit 404 receives the f _DL ⁽²⁾ from the wireless terminal 103 after the process of step S504. May be received. It is also possible to perform steps S503 and S505 at the same time.

  FIG. 8 shows a sequence diagram of calibration processing by the base station 101, the transmission / reception points 102 # 1 and 102 # 2, and the wireless terminal 103.

  In steps S801 # 1 and S801 # 2, self-calibration is performed at the transmission / reception points 102 # 1 and 102 # 2. Steps S801 # 1 and S801 # 2 may correspond to step S501.

In step S802 # 1, transmits a calibration signal from the transceiver point 102 # 1 to the radio terminal 103, in step S803 # 1, _f ^{DL (1)} is obtained as a result estimated by the DL channel estimation in a wireless terminal 103. Steps S802 # 1 and S803 # 1 may correspond to step S502.

In step S802 # 2, a calibration signal is transmitted from the transmission / reception point 102 # 2 to the wireless terminal 103. In step S803 # 2, the wireless terminal 103 performs DL channel estimation to calculate f _DL ⁽²⁾ . Steps S802 # 2 and S803 # 2 may correspond to step S504.

In step S804 # 1, a calibration signal is transmitted from the wireless terminal 103 to the transmission / reception point 102 # 1. The calibration signal received at the transmission / reception point 102 # 1 is converted into a baseband signal, and is output to the baseband unit 301 # 1 in step S805 # 1. In step S806 # 1, UL channel estimation is performed, and f _UL ⁽¹⁾ is obtained as an estimation result. Step S804 # 1 and step S805 # 1 may correspond to step S503.

In step S804 # 2, a calibration signal is transmitted from the wireless terminal 103 to the transmission / reception point 102 # 2. The calibration signal received at the transmission / reception point 102 # 2 is converted into a baseband signal, and is output to the baseband unit 301 # 2 in step S805 # 2. In step S806 # 2, UL channel estimation is performed, and f _UL ⁽²⁾ is calculated. Step S804 # 2 and step S805 # 2 may correspond to step S505.

In step S807, f _DL ⁽¹⁾ and f _DL ^{(2), which} are the DL channel estimation results, are transmitted to, for example, the transmission / reception point 102 # 1. Instead of being transmitted to the transmission / reception point 102 # 1, _fDL ⁽¹⁾ and _fDL ⁽²⁾ may be transmitted to the transmission / reception point 102 # 2. Moreover, you may transmit to the 3rd radio | wireless installation which can communicate with the base station 101. FIG. For example, f _DL ⁽¹⁾ and f _DL ⁽²⁾ transmitted to the transmission / reception point 102 # 1 are transmitted to the base station 101 in step S808. Steps S807 and S808 may correspond to step S506.

When the processing up to step S808 is completed, f _UL ⁽¹⁾ , f _UL ⁽²⁾ , f _DL ^(1), and f _DL ⁽²⁾ are output to the inter-RRH calibration unit of the base station 101. In step S809, RRH calibration coefficients are calculated and set, for example, in the precoders 401 # 1 and 402 # 2, and the precoding matrix is multiplied by the RRH calibration coefficients. Step S809 may correspond to step S507.

  9 and 10 are diagrams illustrating the operation of the RRH calibration unit 404 from another aspect. First, FIG. 9 will be referred to. As indicated by dotted lines 901 and 902, the inter-RRH calibration unit 404 performs transmission by beam forming from the baseband unit 301 # 1, and transmits a calibration signal to the wireless terminal 103. At this time, gain by beam forming is generated as indicated by reference numeral 903. As a result, the wireless terminal 103 can receive a calibration signal having a high intensity, and can estimate the channel state more accurately.

  Similarly, the inter-RRH calibration unit 404 performs transmission by beam forming from the baseband unit 301 # 2 as indicated by alternate long and short dash lines 904 and 905, and transmits a calibration signal to the wireless terminal 103. At this time, gain by beam forming is generated as indicated by reference numeral 906. As a result, the wireless terminal 103 can receive a calibration signal having a high intensity, and can estimate the channel state more accurately.

  Reference is now made to FIG. The wireless terminal 103 transmits a calibration signal to the transmission / reception points 102 # 1 and 102 # 2. When the baseband unit 301 # 1 receives by beam forming and receives the calibration signals 1001 and 1002, a gain is generated by beam forming (see reference numeral 1003 in FIG. 10). Thereby, even if the transmission power of radio terminal 103 is not large, baseband section 301 # 2 can obtain reception power sufficient to perform channel estimation.

  Similarly, when baseband section 301 # 2 receives by beam forming and receives calibration signals 1004 and 1005, a gain is generated by beam forming (see reference numeral 1006 in FIG. 10). Thereby, even if the transmission power of radio terminal 103 is not large, baseband section 301 # 2 can obtain reception power sufficient to perform channel estimation.

  As described above, according to the present embodiment, the RRH calibration is performed by performing the beam forming. For this reason, even if each transmission / reception point includes a plurality of transmission units and reception units, calibration between RRHs can be performed in a shorter time compared to calibration of individual transmission units and reception units. Further, since beam forming is performed after performing self-calibration, a calibration signal having a sufficiently large received power can be transmitted and received, and more accurate calibration between RRHs can be performed.

  In the above description, it is assumed that the transmission / reception points 102 # 1 and 102 # 2 are controlled by the same base station 101. Without being limited to the premise, for example, as shown in FIG. 11, the transmission / reception points 102 # 1 and 102 # 2 may be controlled by different base stations 101 # 1 and 101 # 2. In this case, the inter-RRH calibration unit 404 can be provided in the upper base station 1101 of the base stations 101 # 1 and 101 # 2.

When the number of transmission / reception points is N (N is an integer of 2 or more), for an integer n of 2 or more and N or less,

c _{# n} / c _{# 1} = ( _fDL ^{(# 1)} / _fUL ^{(# 1)} ) / ( _fDL ^(#n) / _fUL ^(#n) )

Thus, the RRH calibration unit 404 can calculate the calibration coefficient related to the transmission / reception point 102 # n.

(Embodiment 2)
As a second embodiment, a mode in which calibration between RRHs is performed between transmission and reception points without using the wireless terminal 103 will be described.

  FIG. 12 is an overall view of a wireless communication system according to the second embodiment. As illustrated in FIG. 12, the wireless communication system 1200 includes a base station 101 and transmission / reception points 102 # 1, 102 # 2, and 102 # 3. Note that the number of transmission / reception points 102 is not limited to three, but may be two or more.

  In the present embodiment, the point that self-calibration is performed at each transmission / reception point 102 and the point that beam forming is performed in the calibration between RRHs are the same as those in the first embodiment. The difference between the second embodiment is that the RRH calibration is first performed between the transmission / reception point 102 # 1 and the transmission / reception point 102 # 2. Next, RRH calibration is performed between the transmission / reception point 102 # 2 and the transmission / reception point 102 # 3. Then, the RRH calibration of the transmission / reception points 102 # 1 to 102 # 3 is performed using the result of the calibration between the RRHs.

  FIG. 13 is a functional block diagram of the base station 101 and the transmission / reception point 102 according to the present embodiment. Except that the number of transmission / reception points 102, the number of self-calibration units 403, and the number of baseband units 301 are increased to 3, the same as in the first embodiment. However, the present embodiment is different from the first embodiment in the operation of the RRH calibration unit 404.

  FIG. 14 is a flowchart illustrating calibration processing according to the present embodiment.

  In step S1401, self-calibration of each transmission / reception point 102 is performed. Self-calibration may be performed in parallel or sequentially.

  In step S1402, the RRH calibration unit 404 performs beam forming from the transmission / reception point 102 # 1 to the transmission / reception point 102 # 2, and transmits a calibration signal. In step S1403, the transmission / reception point 102 # 2 performs beam forming and receives a calibration signal from the transmission / reception point 102 # 1.

Through steps S1402 and S1403, T ₁ ⁽¹⁾ × h ₁₂ × R ₁ ⁽²⁾ is estimated by the baseband unit 301 # 2 and acquired by the inter-RRH calibration unit 404. However, T ₁ ⁽¹⁾ is a response characteristic of the transmission unit 302 # 1 of the transmission / reception point 102 # 1, and h ₁₂ is a channel state between the transmission / reception point 102 # 1 and the transmission / reception point 102 # 2. R ₁ ⁽²⁾ is a response characteristic of the reception unit 303 # 1 of the transmission / reception point 102 # 2.

  Next, in step S1404, the inter-RRH calibration unit 404 performs beam forming from the transmission / reception point 102 # 2 to the transmission / reception point 102 # 1, and transmits a calibration signal. In step S1405, the transmission / reception point 102 # 1 performs beam forming and receives a calibration signal from the transmission / reception point 102 # 2.

Through steps S1404 and S1405, T ₁ ⁽²⁾ × h ₁₂ × R ₁ ⁽¹⁾ is estimated by the baseband unit 301 # 1 and acquired by the inter-RRH calibration unit 404. However, T ₁ ⁽²⁾ is a response characteristic of the transmission unit 302 # 1 of the transmission / reception point 102 # 2, and R ₁ ⁽¹⁾ is a response characteristic of the reception unit 303 # 1 of the transmission / reception point 102 # 1.

Next, in step S1406, the inter-RRH calibration unit 404 calculates the calibration coefficient c _{# 2} / c _{# 1} of the transmission / reception point 102 # 2 with respect to the transmission / reception point 102 _{# 1} as (T ₁ ⁽¹⁾ × h _{12 ^{× R 1 (2)) /}} (T 1 (2) × h 12 × R 1 (1)) is calculated by. The _{c #} 2 / c _{# 1} is equal to ^{_{(T 1 (1) × h}} 12 × R 1 (2)) / (T 1 (2) × h 12 × R 1 (1)) is as follows .

(T ₁ ⁽¹⁾ × h ₁₂ × R ₁ ⁽²⁾ ) / (T ₁ ⁽²⁾ × h ₁₂ × R ₁ ⁽¹⁾ )
= (T ₁ ⁽¹⁾ × R ₁ ⁽²⁾ ) / (T ₁ ⁽²⁾ × R ₁ ⁽¹⁾ )
= (T ₁ ⁽¹⁾ / R ₁ ⁽¹⁾ ) / (T ₁ ⁽²⁾ / R ₁ ⁽²⁾ )
= C _{# 2} / c _{# 1}

  Next, in step S1407, the RRH calibration unit 404 performs beamforming from the transmission / reception point 102 # 2 and transmits a calibration signal to the transmission / reception point 102 # 3. In step S1408, transmission / reception point 102 # 3 performs beam forming and receives a calibration signal from transmission / reception point 102 # 2.

Through steps S1407 and S1408, T ₁ ⁽²⁾ × h ₂₃ × R ₁ ⁽³⁾ is estimated by the baseband unit 301 # 3 and acquired by the inter-RRH calibration unit 404. _{However, h 23} is the channel state between the transmitting and receiving point 102 # 2 and receiving point 102 # _3, ^{R 1 (3)} is the response characteristic of the receiving section 303 # 1 transceiver point 102 # 3.

  Next, in step S1409, the RRH calibration unit 404 performs beamforming from the transmission / reception point 102 # 3 and transmits a calibration signal to the transmission / reception point 102 # 2. In step S1410, transmission / reception point 102 # 2 performs beamforming and receives a calibration signal from transmission / reception point 102 # 3.

Through steps S1409 and S1410, T ₁ ⁽³⁾ × h ₂₃ × R ₁ ⁽²⁾ is estimated by the baseband unit 301 # 2 and acquired by the inter-RRH calibration unit 404. However, T ₁ ⁽³⁾ is a response characteristic of the transmission unit 302 # 1 of the transmission / reception point 102 # 3.

Next, in step S1411, the calibration unit 404 between RRH, calibration coefficients of the transmitting and receiving point 102 # 3 relative to the receiving point 102 # 2 _c # 3 / _{c # 2} and ^{_{(T 1 (2) × h}} 12 ^{_{× R 1 (3)) /}} (T 1 (3) × h 12 × R 1 (2)) is calculated by. _{c #} 3 / c _{# 2} is ^{_{(T 1 (2) × h}} 12 × R 1 (3)) / (T 1 (3) × h 12 × R 1 (2)) and equal, at step S1406 It is the same as described.

Next, in step S1412, the RRH calibration unit 404 calculates the calibration coefficient c _{# 3} / c _{# 1} of the transmission / reception point 102 # 3 with respect to the transmission / reception point 102 _{# 1} as (c _{# 3} / c _{# 2).} ) × (c _{# 2} / c _{# 1} ).

  The execution of each calibration step is not limited to the order shown in the flowchart of FIG. For example, S1402 and S1403, and S1404 and S1405 may be executed in an arbitrary order until the process of step S1406. Further, S1407 and S1408 and S1409 and S1410 can be executed in an arbitrary order until the processing of step S1411. Further, step S1411 may be executed before step S1406.

  FIG. 15 shows a sequence diagram of calibration processing by the base station 101 and the transmission / reception points 102 # 1 to 102 # 3.

  In steps S1501 # 1, S1501 # 2, and S1501 # 3, self-calibration is performed at the transmission / reception points 102 # 1 to 102 # 3. Steps S1501 # 1, S1501 # 2, and S1501 # 3 may correspond to step S1401.

  In step S1502, beam forming is performed from the transmission / reception point 102 # 1, and a calibration signal is transmitted to the transmission / reception point 102 # 2. The transmission / reception point 102 # 2 performs beam forming and receives a calibration signal from the transmission / reception point 102 # 1. In step S1503, the baseband signal corresponding to the received calibration signal is transmitted from the transmission / reception point 102 # 2 to the baseband unit 301 # 2 of the base station 101. In step S1504, channel estimation is performed in baseband section 301 # 2. Steps S1502 to S1504 may correspond to steps S1402 and S1403.

  In step S1505, beam forming is performed from the transmission / reception point 102 # 2, and a calibration signal is transmitted to the transmission / reception point 102 # 1. The transmission / reception point 102 # 1 performs beam forming and receives a calibration signal from the transmission / reception point 102 # 2. In step S1506, the baseband signal corresponding to the received calibration signal is transmitted from the transmission / reception point 102 # 1 to the baseband unit 301 # 1 of the base station 101. In step S1507, channel estimation is performed in baseband section 301 # 1. Steps S1505 to S1507 may correspond to steps S1404 and S1405.

  In step S1508, beam forming is performed from transmission / reception point 102 # 3, and a calibration signal is transmitted to transmission / reception point 102 # 2. The transmission / reception point 102 # 2 performs beam forming and receives a calibration signal from the transmission / reception point 102 # 3. In step S1509, the baseband signal corresponding to the received calibration signal is transmitted from the transmission / reception point 102 # 2 to the baseband unit 301 # 2 of the base station 101. In step S1510, the baseband unit 301 # 2 receives the channel. An estimate is made. Steps S1508 to S1510 may correspond to steps S1409 and S1410.

  In step S1511, beam forming is performed from transmission / reception point 102 # 2, and a calibration signal is transmitted to transmission / reception point 102 # 3. The transmission / reception point 102 # 3 performs beam forming and receives a calibration signal from the transmission / reception point 102 # 2. In step S1512, the baseband signal corresponding to the received calibration signal is transmitted from the transmission / reception point 102 # 2 to the baseband unit 301 # 3. In step S1513, the baseband unit 301 # 3 performs channel estimation. . Steps S1511 to S1513 may correspond to steps S1407 and S1408.

  In step S1514, a calibration coefficient is calculated. Step S1514 may correspond to steps S1406, S1411, and S1412.

  As described above, in the present embodiment, RRH calibration can be performed using transmission / reception points, and unlike the first embodiment, the use of a wireless terminal can be eliminated. In addition, since the position of the transmission / reception point is usually fixed, beam forming can be performed more accurately than when a movable wireless terminal is used, and calibration can be performed more accurately.

When the number of transmission / reception points is N (N is an integer of 2 or more), for an integer n of 2 or more and N or less,

_{c #n / c # n-1} = (T 1 (n-1) × h n-1n × R 1 (n)) / (T 1 (n) × h n-1n × R 1 (n-1) )

To calculate the RRH calibration unit 404,

_{c #n / c # 1 = (} c #n / c # n-1) × (c # n-1 / c # n-2) × ... × (c # 2 / c # 1)

To calculate the calibration coefficient.

_{Incidentally, c # 2 / c # 1} , c # 3 / c # 2, ..., is not necessary to calculate the _{c # n-1 / c #} n-2, c #n / c # n-1 in this order . For _example, determine the _{c #} 2 / _c # ₁ and _c #n _{/ c # n-1} in parallel, then _{c #} 3 / _{c # 2} and _{c # n-1 / c #} n-2 to determine in parallel Thus, the time required for calibration between RRHs can be shortened.

(Embodiment 3)
As the third embodiment, RRH calibration combining the first embodiment and the second embodiment will be described.

  FIG. 16 is a sequence diagram illustrating calibration processing by the base station 101, the transmission / reception points 102 # 1 to 102 # 3, and the wireless terminal 103 in the third embodiment.

  In steps S801 # 1 to S801 # 3, self-calibration is performed at each of the transmission / reception points 102 # 1 to 102 # 3.

  In step S802 # 1, a calibration signal is transmitted from the transmission / reception point 102 # 1 to the radio terminal 103, and in step S803 # 1, the baseband unit 314 of the radio terminal 103 performs DL channel estimation.

  In step S802 # 2, a calibration signal is transmitted from the transmission / reception point 102 # 2 to the radio terminal 103, and in step S803 # 2, the baseband unit 314 of the radio terminal 103 performs DL channel estimation.

  In step S802 # 3, beam forming is performed from the transmission / reception point 102 # 3, and a calibration signal is transmitted to the wireless terminal 103. In step S803 # 3, the baseband unit 314 of the wireless terminal 103 performs DL channel estimation.

  In step S804 # 1, a calibration signal is transmitted from the wireless terminal 103 to the transmission / reception point 102 # 1, and the transmission / reception point 102 # 1 receives the calibration signal by beam forming. In step S805 # 1, a baseband signal corresponding to the received calibration signal is transmitted to baseband section 301 # 1. In step S806 # 1, UL channel estimation is performed by the baseband unit 301 # 1.

  In step S804 # 2, a calibration signal is transmitted from the wireless terminal 103 to the transmission / reception point 102 # 2, and the transmission / reception point 102 # 2 receives the calibration signal by beam forming. In step S805 # 2, a baseband signal corresponding to the received calibration signal is transmitted to baseband section 301 # 2. In step S806 # 2, the baseband unit 301 # 2 performs UL channel estimation.

  In step S804 # 3, a calibration signal is transmitted from the wireless terminal 103 to the transmission / reception point 102 # 3, and the transmission / reception point 102 # 3 receives the calibration signal by beam forming. In step S805 # 3, a baseband signal corresponding to the received calibration signal is transmitted to baseband section 301 # 3. In step S806 # 3, the baseband unit 301 # 3 performs UL channel estimation.

  In step S807, the result of DL channel estimation is transmitted from the wireless terminal 103 to, for example, the transmission / reception point 102 # 1, and the result of DL channel estimation is transmitted to the base station 101 in step S808.

  Steps S802 # 1 to S807 are processes corresponding to the first embodiment, and can be repeatedly executed a number of times corresponding to the number of wireless terminals 103. By using a plurality of wireless terminals 103, the accuracy of calibration can be increased.

  Steps S1502 to S1513 are processes corresponding to the second embodiment, and have already been described.

  In step S1601, a calibration coefficient is calculated. In the present embodiment, calculation of a calibration coefficient corresponding to the first embodiment and calculation of a calibration coefficient corresponding to the second embodiment are performed. Therefore, the calibration coefficient can be calculated by an arithmetic average, or can be calculated by arbitrarily weighting. As a result, the calibration coefficient can be calculated more accurately.

(Hardware configuration)
FIG. 17A is a hardware configuration diagram of the base station 101 and the transmission / reception point 102.

  The base station 101 includes a processor 1701, a memory 1702, an LSI (Large Scale Integrated circuit) 1703, and an NIF (Network Interface Face) circuit 1704. The transmission / reception point 102 # i includes an RF circuit 1705 # i (i is a natural number).

  The memory 1702 includes a volatile storage device such as a DRAM (Dynamic Random Memory) and a nonvolatile storage device such as a hard disk, an optical disk, or a magneto-optical disk. The memory 1702 can store a program, and the processor 1701 executes the program to control each unit of the base station 101 and input / output data. The memory 1702 provides a work area necessary for executing the program and can store various setting parameters of the base station 101 and the transmission / reception point 102 # i.

  The LSI 1703 functions as a signal processor, and can operate as the baseband unit 301, for example. The NIF circuit 1704 is a circuit for realizing the core network interface 402.

  Instead of executing the program by the processor 1701, control equivalent to the program can be realized by hardware using an FPGA (Field Programmable Gate Array). By using the FPGA, the base station 101 can be realized without using a program.

  The RF circuit 1705 # i can be realized by combining a circuit that converts a baseband signal and a radio signal and a radio circuit that processes the radio signal.

  FIG. 17B is a hardware configuration diagram of the wireless terminal 103.

  The wireless terminal 103 includes a processor 1711, a memory 1712, an RF circuit 1714, and an LSI 1713.

  The memory 1712 includes a volatile storage device such as a DRAM and a nonvolatile storage device such as a hard disk, an optical disk, or a magneto-optical disk. The memory 1712 can store a program, and the processor 1711 executes the program to control each unit of the wireless terminal 103 and input / output data. The memory 1712 provides a work area necessary for executing the program, and can store various setting parameters of the wireless terminal 103.

  The LSI 1713 functions as a signal processor, and can operate as the baseband unit 314, for example.

  The RF circuit 1714 can be realized by combining a circuit that performs conversion between a baseband signal and a radio signal and a radio circuit that processes the radio signal.

  Instead of executing the program by the processor 1711, control equivalent to the program can be realized by hardware using an FPGA. By using the FPGA, the wireless terminal 103 can be realized without using a program.

Regarding the above embodiment, the following additional notes are disclosed.
(Appendix 1)
A base station connected to a plurality of transmission / reception points,
A base station comprising a calibrator that calculates a calibration coefficient for correcting a weight in the beamforming communication of each of the plurality of transmission / reception points based on the beamforming communication of each of the plurality of transmission / reception points.

(Appendix 2)
The base station according to appendix 1, wherein the beamforming communication of each of the plurality of transmission / reception points is time division multiplex communication.

(Appendix 3)
The beam forming communication of each of the plurality of transmission / reception points is communication between a wireless device located in the base station and the plurality of transmission / reception points,
The calibrator calculates the calibration coefficient based on downlink radio characteristics from each of the plurality of transmission / reception points to the radio apparatus and uplink radio characteristics from the radio apparatus to each of the plurality of transmission / reception points. 2. The base station according to 2.

(Appendix 4)
Wherein the plurality of the number of transmitting and receiving points is N, the downstream radio characteristics from each of the plurality of transmission and reception points to the wireless device _{^{f DL (1), f DL}} (2), f DL (3), ... and _{f DL} ^{( N),} and the uplink radio characteristics from the wireless device to each of the plurality of transmission / reception points are f _UL ⁽¹⁾ , f _UL ⁽²⁾ , f _UL ⁽³⁾ ,... And f _UL ^(N) ,
The calibrators, the calibration factor ^{c _(1),} as ^{c (2), c (3} ), ... and ^{c (N),}
c ⁽¹⁾ = 1,
c ⁽²⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ),
c ⁽³⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽³⁾ / _fDL ⁽³⁾ ),
... and c ^(N) = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ^(N) / _fDL ^(N) )
The base station according to appendix 3, which calculates

(Appendix 5)
The plurality of transmission / reception points are RRH ⁽¹⁾ , RRH ⁽²⁾ , RRH ⁽³⁾ ,... And RRH ^(N), and the beamforming communication by each of the plurality of transmission / reception points is RRH ⁽¹⁾ and RRH ^{(2 ). )} , RRH ⁽²⁾ and RRH ⁽³⁾ ,..., RRH ^(N−1) and RRH ^(N), respectively, and the radio characteristics from RRH ^{(i )} to RRH ^{(i + 1) are} expressed as f _DL ^{( i)} and the radio characteristics from RRH ^{(i + 1)} to RRH ⁽ⁱ⁾ are f _UL ⁽ⁱ⁾ ,
The calibrator uses coefficients c ⁽¹⁾ _, c ⁽²⁾ , c ⁽³⁾ ,... And c ^(N) as
c ⁽¹⁾ = 1,
c ⁽²⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ),
c ⁽³⁾ = ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ) / ( _fUL ⁽³⁾ / _fDL ⁽³⁾ ),
... and c ^(N) = ( _fUL ^(N-1) / _fDL ^(N-1) ) / ( _fUL ^(N) / _fDL ^(N) )
And the calibration coefficient is
c ⁽¹⁾ ,
c ⁽²⁾ xc ⁽¹⁾ ,
c ⁽³⁾ xc ⁽²⁾ xc ⁽¹⁾ ,
... and c ^(N) xc ^(N-1) x ... xc ⁽¹⁾
The base station according to appendix 1 or 2 for calculating

(Appendix 6)
A wireless communication system comprising a plurality of transmission / reception points and a base station connected to the plurality of transmission / reception points,
A wireless communication system including a calibrator that calculates a calibration coefficient for correcting a weight in the beam forming communication of each of the plurality of transmission / reception points based on the beam forming communication of each of the plurality of transmission / reception points.

(Appendix 7)
The wireless communication system according to appendix 6, wherein the beamforming communication of each of the plurality of transmission / reception points is time division multiplex communication.

(Appendix 8)
The beamforming communication of each of the plurality of transmission / reception points is communication between a wireless terminal located in the base station and the plurality of transmission / reception points,
The calibrator calculates the calibration coefficient based on a downlink radio characteristic from each of the plurality of transmission / reception points to the radio apparatus and an uplink radio characteristic from the radio apparatus to each of the plurality of transmission / reception points. 8. The wireless communication system according to 7.

(Appendix 9)
Wherein the plurality of the number of transmitting and receiving points is N, the downstream radio characteristics from each of the plurality of transmission and reception points to the wireless device _{^{f DL (1), f DL}} (2), f DL (3), ... and _{f DL} ^{( N),} and the uplink radio characteristics from the wireless device to each of the plurality of transmission / reception points are f _UL ⁽¹⁾ , f _UL ⁽²⁾ , f _UL ⁽³⁾ ,... And f _UL ^(N) ,
The calibrators, the calibration factor ^{c _(1),} as ^{c (2), c (3} ), ... and ^{c (N),}
c ⁽¹⁾ = 1,
c ⁽²⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ),
c ⁽³⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽³⁾ / _fDL ⁽³⁾ ),
... and c ^(N) = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ^(N) / _fDL ^(N) )
The wireless communication system according to attachment 8, wherein

(Appendix 10)
The plurality of transmission / reception points are RRH ⁽¹⁾ , RRH ⁽²⁾ , RRH ⁽³⁾ ,... And RRH ^(N), and the beamforming communication by each of the plurality of transmission / reception points is RRH ⁽¹⁾ and RRH ^{(2 ). )} , RRH ⁽²⁾ and RRH ⁽³⁾ ,..., RRH ^(N−1) and RRH ^(N), respectively, and the radio characteristics from RRH ^{(i )} to RRH ^{(i + 1) are} expressed as f _DL ^{( i)} and the radio characteristics from RRH ^{(i + 1)} to RRH ⁽ⁱ⁾ are f _UL ⁽ⁱ⁾ ,
The calibrator uses coefficients c ⁽¹⁾ _, c ⁽²⁾ , c ⁽³⁾ ,... And c ^(N) as
c ⁽¹⁾ = 1,
c ⁽²⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ),
c ⁽³⁾ = ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ) / ( _fUL ⁽³⁾ / _fDL ⁽³⁾ ),
... and c ^(N) = ( _fUL ^(N-1) / _fDL ^(N-1) ) / ( _fUL ^(N) / _fDL ^(N) )
And the calibration coefficient is
c ⁽¹⁾ ,
c ⁽²⁾ xc ⁽¹⁾ ,
c ⁽³⁾ xc ⁽²⁾ xc ⁽¹⁾ ,
... and c ^(N) xc ^(N-1) x ... xc ⁽¹⁾
The wireless communication system according to appendix 6 or 7, which calculates

(Appendix 11)
A calibration method of a wireless communication system comprising a base station connected to a plurality of transmission / reception points,
Beam forming communication is performed from each of the plurality of transmission / reception points,
A calibration method for a wireless communication system, wherein a calibration coefficient for correcting a weight in the beamforming communication at each of the plurality of transmission / reception points is calculated based on beamforming communication at each of the plurality of transmission / reception points.

(Appendix 12)
The wireless communication system calibration method according to appendix 11, wherein the beamforming communication of each of the plurality of transmission / reception points is time division multiplex communication.

(Appendix 13)
The beam forming communication of each of the plurality of transmission / reception points is communication between a wireless device located in the base station and the plurality of transmission / reception points,
The calibration coefficient is calculated based on a downlink radio characteristic from each of the plurality of transmission / reception points to the radio apparatus and an uplink radio characteristic from the radio apparatus to each of the plurality of transmission / reception points. A calibration method for a wireless communication system.

(Appendix 14)
Wherein the plurality of the number of transmitting and receiving points is N, the downstream radio characteristics from each of the plurality of transmission and reception points to the wireless device _{^{f DL (1), f DL}} (2), f DL (3), ... and _{f DL} ^{( N),} and the uplink radio characteristics from the wireless device to each of the plurality of transmission / reception points are f _UL ⁽¹⁾ , f _UL ⁽²⁾ , f _UL ⁽³⁾ ,... And f _UL ^(N) ,
As the calibration coefficients c ⁽¹⁾ _, c ⁽²⁾ , c ⁽³⁾ ,... And c ^(N) ,
c ⁽¹⁾ = 1,
_{^{c (2) = (f UL}} (1) / f DL (1)) / (f UL (2) / f DL (2)),
c ⁽³⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽³⁾ / _fDL ⁽³⁾ ),
... and c ^(N) = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ^(N) / _fDL ^(N) )
The wireless communication system calibration method according to attachment 13, wherein the wireless communication system is calculated.

(Appendix 15)
Wherein the plurality of the transmitting and receiving points ^{RRH (1), RRH (2} ), RRH (3), ... and the ^{RRH (N),} the beam forming communication by the plurality of receiving points, ^{RRH (1)} and RRH ^{(2 )} , RRH ⁽²⁾ and RRH ⁽³⁾ ,..., RRH ^(N−1) and RRH ^(N), respectively, and the radio characteristics from RRH ^{(i )} to RRH ^{(i + 1) are} expressed as f _DL ^{( i)} and the radio characteristics from RRH ^{(i + 1)} to RRH ⁽ⁱ⁾ are f _UL ⁽ⁱ⁾ ,
As coefficients c ⁽¹⁾ _, c ⁽²⁾ , c ⁽³⁾ ,... And c ^(N) ,
c ⁽¹⁾ = 1,
c ⁽²⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ),
c ⁽³⁾ = ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ) / ( _fUL ⁽³⁾ / _fDL ⁽³⁾ ),
... and c ^(N) = ( _fUL ^(N-1) / _fDL ^(N-1) ) / ( _fUL ^(N) / _fDL ^(N) )
And the calibration coefficient is
c ⁽¹⁾ ,
c ⁽²⁾ xc ⁽¹⁾ ,
c ⁽³⁾ xc ⁽²⁾ xc ⁽¹⁾ ,
... and c ^(N) xc ^(N-1) x ... xc ⁽¹⁾
The calibration method of the radio | wireless communications system of Additional remark 11 or 12 which computes.

DESCRIPTION OF SYMBOLS 100 Wireless communication system 101 Base station 102 # 1, 102 # 2, 102 # 3 Transmission / reception point 103 Wireless terminal 301 # 1, 301 # 2, 301 # 3 Baseband part 302 # 1, 302 # 2 Transmission part 303 # 1, 303 # 2 receiving unit 304 # 1, 304 # 2 antenna 311 transmitting unit 312 receiving unit 313 antenna 314 baseband unit 401 # 1, 401 # 2, 401 # 3 precoder 402 core network interface 403 # 1, 403 # 2, 403 # 3 Self-calibration unit 404 RRH calibration unit

The transmission / reception point 102 includes a transmission unit 302 # 1, a reception unit 303 # 1, and a transmission unit 302 # 2 and a reception unit 303 # 2, corresponding to the antennas 304 # 1 and 304 # 2. In addition, the base station 101 includes a baseband unit 301. Further, the wireless terminal 103 includes a transmitting unit 311, a receiving unit 312, a baseband unit 3 14.

Let f _DL ^{(1) be} a channel state estimated by the baseband unit 314 of the wireless terminal 103 from the input of the baseband signal to the transmission unit 302 # 1 to the output of the baseband signal of the reception unit 312. Also, let f _DL ^{(2) be} a channel state estimated by the baseband unit 314 of the wireless terminal 103, from the input of the baseband signal to the transmission unit 302 # 2 to the output of the baseband signal of the reception unit 312. At this time, f _DL ⁽¹⁾ and f _DL ⁽²⁾ are as follows.

^{_{f DL (1) = T 1}} × h 1 × r 1 ( Equation 1)
f _DL ⁽²⁾ = T ₂ × h ₂ × r ₁ (Formula 2)

Also, let f _UL ^{(1) be} the channel state estimated by the baseband unit 301 of the base station 101 from the input of the baseband signal to the transmission unit 311 to the output of the baseband signal of the reception unit 303 # 1. Also, let f _UL ^{(2) be} the channel state estimated by the baseband unit 301 of the base station 101 from the input of the baseband signal to the transmission unit 311 to the output of the baseband signal of the reception unit 303 # 2. At this time, f _UL ⁽¹⁾ and f _UL ⁽²⁾ are as follows.

f _UL ⁽¹⁾ = t ₁ × h ₁ × R ₁ (Formula 3)
f _UL ⁽²⁾ = t ₁ × h ₂ × R ₂ (Formula 4)

Therefore, if any one of T ₁ ≠ R ₁ , T ₂ ≠ R ₂ , t ₁ ≠ r ₁ and t ₂ ≠ r ₂ holds, f _DL ⁽¹⁾ = f _UL ⁽¹⁾ and f _DL ^{( 2)} = f _UL ⁽²⁾ does not always hold. For this reason, the DL radio link channel and the UL radio link channel cannot be identified. Therefore, even if the channel state of the DL radio channel is estimated based on the estimation of the channel state of the UL radio channel, the estimation is not correct, precoding in the DL radio channel is not optimal, and communication characteristics deteriorate. .

Each of the self-calibration units 403 # 1 and 403 # 2 outputs a self-calibration coefficient calculated from u ₁ and u ₂ to each of the precoders 401 # 1 and 40 1 # 2. Thus, for example, when the precoders 401 # 1 and 40 1 # 2 perform precoding, the baseband signal transmitted to the transmission unit 302 # 2 is multiplied by the weight, and is further multiplied by u ₂ / u _1. Become.

Similarly, f _UL ^{(# 2)} is a channel state from the input of the baseband signal of the transmission unit 311 of the wireless terminal 103 to the output of the baseband signal of the precoder 401 # 2 of the base station 101,

f _UL ^{(# 2)} = t ₁ × (h ₁ ^{(# 2)} × R ₁ ^{(# 2)} × W ₁ ^{(# 2)} + h ₂ ^{(# 2)} × R ₂ ^{(# 2)} × W ₂ ^{(# 2 ))} (equation 8)

It can be. However, R ₁ ^{( # 2)} and R ₂ ^{(# 2)} are response characteristics of the receiving units 303 # 1 and 303 # 2 of the transmission / reception point 102 # 2.

For example, after completion of the self-calibration , the equation T ₁ ^(#n) / R ₁ ^(#n) = T ₂ ^(#n) / R ₂ ^(#n) = k _{# with} respect to the constant k _#n . _n . Therefore, the equation ^{_{f DL (#n) / f UL}} (#n) = k #n × r 1 / t 1. Therefore, _{c #} 2 / _c # ₁ is represented as _{k # 1 / k # 2,} t 1, r 1, h 1 (# 1), h 1 (# 2), h 2 (# 1), h ₂ ^{(# 2)} , W ₁ ^{(# 1)} , W ₁ ^{(# 2)} , W ₂ ^{(# 1),} and W ₂ ^{(# 2)} do not depend .

FIG. 6 shows one procedure of self-calibration by the self-calibration unit 403. First, as indicated by the one-dot chain line 601, a calibration signal is transmitted from the transmission unit 302 # 1, received by the reception unit 303 # 2, and T ₁ × H × R ₂ is calculated. Next, as indicated by the dotted line 602, a calibration signal is transmitted from the transmission unit 302 # 2, received by the reception unit 303 # 1, and T ₂ × H × R ₁ is calculated. H is the channel state between antennas 304 # 1 and 30 4 # 2. By dividing T ₁ × H × R ₂ by T ₂ × H × R ₁ , (T ₁ / R ₁ ) / (T ₂ / R ₂ ) is obtained.

When the processing up to step S808 is completed, f _UL ⁽¹⁾ , f _UL ⁽²⁾ , f _DL ^(1), and f _DL ⁽²⁾ are output to the inter-RRH calibration unit 404 of the base station 101. In step S809, RRH calibration coefficients are calculated and set, for example, in the precoders 401 # 1 and 402 # 2, and the precoding matrix is multiplied by the RRH calibration coefficients. Step S809 may correspond to step S507.

Similarly, the inter-RRH calibration unit 404 performs transmission by beam forming from the baseband unit 301 # 2 as indicated by two- dot chain lines 904 and 905, and transmits a calibration signal to the wireless terminal 103. At this time, gain by beam forming is generated as indicated by reference numeral 906. As a result, the wireless terminal 103 can receive a calibration signal having a high intensity, and can estimate the channel state more accurately.

Reference is now made to FIG. The wireless terminal 103 transmits a calibration signal to the transmission / reception points 102 # 1 and 102 # 2. When the baseband unit 301 # 1 receives by beam forming and receives the calibration signals 1001 and 1002, a gain is generated by beam forming (see reference numeral 1003 in FIG. 10). Thereby, even if the transmission power of radio terminal 103 is not large, baseband section 301 # 1 can obtain reception power sufficient to perform channel estimation.

When the number of transmission / reception points is N (N is an integer of 2 or more), for an integer n of 2 or more and N or less,

c _{# n} / c _{# 1} = ( _fDL ^{(# 1)} / _fUL ^{(# 1)} ) / ( _fDL ^(#n) / _fUL ^(#n) )

Thus, the RRH calibration unit 404 can calculate the calibration coefficient related to the transmission / reception point 102 # n. The coefficients (1, c) c _{# 2} / c _{# 1} , c _{# 3} / c _{# 1} ,... And c _{# n} / c _{# 1} are calibration coefficients c ⁽¹⁾ , c ⁽²⁾ , c ^{(3 )} ,... And c ^(N) are examples.

In step S1511, beam forming is performed from transmission / reception point 102 # 2, and a calibration signal is transmitted to transmission / reception point 102 # 3. The transmission / reception point 102 # 3 performs beam forming and receives a calibration signal from the transmission / reception point 102 # 2. In step S1512, the baseband signal corresponding to the received calibration signal is transmitted from the transmission / reception point 102 # 3 to the baseband unit 301 # 3. In step S1513, the baseband unit 301 # 3 performs channel estimation. . Steps S1511 to S1513 may correspond to steps S1407 and S1408.

_{Incidentally, c # 2 / c # 1} , c # 3 / c # 2, ..., is not necessary to calculate the _{c # n-1 / c #} n-2, c #n / c # n-1 in this order . For _example, determine the _{c #} 2 / _c # ₁ and _c #n _{/ c # n-1} in parallel, then _{c #} 3 / _{c # 2} and _{c # n-1 / c #} n-2 to determine in parallel Thus, the time required for calibration between RRHs can be shortened. The coefficient _{(1,) c # 2 /} c # 1, c # 3 / c # 2, ... c # n-1 / c # n-2 and _c #n _{/ c # n-1,} the coefficient ^{d ( 1)} , d ⁽²⁾ , d ⁽³⁾ ,... D ^(N−1) and d ^(N) are examples. In other words, the coefficient c ^(N) may be calculated by c ^(N) = d ^(N) × d ^(N−1) ×... × d ⁽¹⁾ .

Memory 1702 is composed of a DRAM (Dynamic Random Access Me m ory ) volatile storage device such as a, and a hard disk, a nonvolatile memory device such as an optical disk or a magneto-optical disk. The memory 1702 can store a program, and the processor 1701 executes the program to control each unit of the base station 101 and input / output data. The memory 1702 provides a work area necessary for executing the program and can store various setting parameters of the base station 101 and the transmission / reception point 102 # i.

(Appendix 4)
Wherein the plurality of the number of transmitting and receiving points is N, the downstream radio characteristics from each of the plurality of transmission and reception points to the wireless device _{^{f DL (1), f DL}} (2), f DL (3), ... and _{f DL} ^{( N),} and the uplink radio characteristics from the wireless device to each of the plurality of transmission / reception points are f _UL ⁽¹⁾ , f _UL ⁽²⁾ , f _UL ⁽³⁾ ,... And f _UL ^(N) ,
The calibrators, the calibration factor ^{c (1),} as ^{c (2), c (3} ), ... and ^{c (N),}
c ⁽¹⁾ = 1,
_{^{c (2) = (f D}} L (1) / f U L (1)) / (f D L (2) / f U L (2)),
_{^{c (3) = (f D}} L (1) / f U L (1)) / (f D L (3) / f U L (3)),
... and _{^{c (N) = (f D}} L (1) / f U L (1)) / (f D L (N) / f U L (N))
The base station according to appendix 3, which calculates

(Appendix 5)
Wherein the plurality of the transmitting and receiving points ^{RRH (1), RRH (2} ), RRH (3), ... and the ^{RRH (N),} the beam forming communication by the plurality of receiving points, ^{RRH (1)} and RRH ^{(2 )} , RRH ⁽²⁾ and RRH ⁽³⁾ ,..., RRH ^(N−1) and RRH ^(N), respectively, and the radio characteristics from RRH ^{(i )} to RRH ^{(i + 1) are} expressed as f _DL ^{( i)} and the radio characteristics from RRH ^{(i + 1)} to RRH ⁽ⁱ⁾ are f _UL ⁽ⁱ⁾ ,
The calibrator is the coefficient d ^(1), as ^{d (2), d (3} ), ... and d ^(N),
d ⁽¹⁾ = 1,
_{^{d (2) = (f D}} L (1) / f U L (1)) / (f D L (2) / f U L (2)),
_{^{d (3) = (f D}} L (2) / f U L (2)) / (f D L (3) / f U L (3)),
…and
_{^{d (N) = (f D}} L (N-1) / f U L (N-1)) / (f D L (N) / f U L (N))
And the calibration coefficients c ⁽¹⁾ , c ⁽²⁾ , c ⁽³⁾ ,... And c ^(N) ,
c ⁽¹⁾ = d ⁽¹⁾
c ⁽²⁾ = d ⁽²⁾ × d ⁽¹⁾ ,
c ⁽³⁾ = d ⁽³⁾ × d ⁽²⁾ × d ⁽¹⁾ ,
... and c ^(N) = d ^(N) x d ^(N-1) x ... x d ⁽¹⁾
The base station according to appendix 1 or 2 for calculating

(Appendix 8)
The beam forming communication of each of the plurality of transmission / reception points is communication between a wireless device located in the base station and the plurality of transmission / reception points,
The calibrator calculates the calibration coefficient based on a downlink radio characteristic from each of the plurality of transmission / reception points to the radio apparatus and an uplink radio characteristic from the radio apparatus to each of the plurality of transmission / reception points. 8. The wireless communication system according to 7.

(Appendix 9)
Wherein the plurality of the number of transmitting and receiving points is N, the downstream radio characteristics from each of the plurality of transmission and reception points to the wireless device _{^{f DL (1), f DL}} (2), f DL (3), ... and _{f DL} ^{( N),} and the uplink radio characteristics from the wireless device to each of the plurality of transmission / reception points are f _UL ⁽¹⁾ , f _UL ⁽²⁾ , f _UL ⁽³⁾ ,... And f _UL ^(N) ,
The calibrators, the calibration factor ^{c (1),} as ^{c (2), c (3} ), ... and ^{c (N),}
c ⁽¹⁾ = 1,
_{^{c (2) = (f D}} L (1) / f U L (1)) / (f D L (2) / f U L (2)),
_{^{c (3) = (f D}} L (1) / f U L (1)) / (f D L (3) / f U L (3)),
... and _{^{c (N) = (f D}} L (1) / f U L (1)) / (f D L (N) / f U L (N))
Calculating a wireless communication system according to Supplementary Note 8.

(Appendix 10)
The plurality of transmission / reception points are RRH ⁽¹⁾ , RRH ⁽²⁾ , RRH ⁽³⁾ ,... And RRH ^(N), and the beamforming communication by each of the plurality of transmission / reception points is RRH ⁽¹⁾ and RRH ^{(2 ). )} , RRH ⁽²⁾ and RRH ⁽³⁾ ,..., RRH ^(N−1) and RRH ^(N), respectively, and the radio characteristics from RRH ^{(i )} to RRH ^{(i + 1) are} expressed as f _DL ^{( i)} and the radio characteristics from RRH ^{(i + 1)} to RRH ⁽ⁱ⁾ are f _UL ⁽ⁱ⁾ ,
The calibrator is the coefficient d ^(1), as ^{d (2), d (3} ), ... and d ^(N),
d ⁽¹⁾ = 1,
_{^{d (2) = (f D}} L (1) / f U L (1)) / (f D L (2) / f U L (2)),
_{^{d (3) = (f D}} L (2) / f U L (2)) / (f D L (3) / f U L (3)),
…and
_{^{d (N) = (f D}} L (N-1) / f U L (N-1)) / (f D L (N) / f U L (N))
And the calibration coefficients c ⁽¹⁾ , c ⁽²⁾ , c ⁽³⁾ ,... And c ^(N) ,
c ⁽¹⁾ = d ⁽¹⁾
c ⁽²⁾ = d ⁽²⁾ × d ⁽¹⁾ ,
c ⁽³⁾ = d ⁽³⁾ × d ⁽²⁾ × d ⁽¹⁾ ,
... and c ^(N) = d ^(N) x d ^(N-1) x ... x d ⁽¹⁾
The wireless communication system according to appendix 6 or 7, which calculates

(Appendix 14)
Wherein the plurality of the number of transmitting and receiving points is N, the downstream radio characteristics from each of the plurality of transmission and reception points to the wireless device _{^{f DL (1), f DL}} (2), f DL (3), ... and _{f DL} ^{( N),} and the uplink radio characteristics from the wireless device to each of the plurality of transmission / reception points are f _UL ⁽¹⁾ , f _UL ⁽²⁾ , f _UL ⁽³⁾ ,... And f _UL ^(N) ,
As the calibration coefficients c ⁽¹⁾ , c ⁽²⁾ , c ⁽³⁾ ,... And c ^(N) ,
c ⁽¹⁾ = 1,
_{^{c (2) = (f D}} L (1) / f U L (1)) / (f D L (2) / f U L (2)),
_{^{c (3) = (f D}} L (1) / f U L (1)) / (f D L (3) / f U L (3)),
... and _{^{c (N) = (f D}} L (1) / f U L (1)) / (f D L (N) / f U L (N))
The wireless communication system calibration method according to attachment 13, wherein the wireless communication system is calculated.

(Appendix 15)
Wherein the plurality of the transmitting and receiving points ^{RRH (1), RRH (2} ), RRH (3), ... and the ^{RRH (N),} the beam forming communication by the plurality of receiving points, ^{RRH (1)} and RRH ^{(2 )} , RRH ⁽²⁾ and RRH ⁽³⁾ ,..., RRH ^(N−1) and RRH ^(N), respectively, and the radio characteristics from RRH ^{(i )} to RRH ^{(i + 1) are} expressed as f _DL ^{( i)} and the radio characteristics from RRH ^{(i + 1)} to RRH ⁽ⁱ⁾ are f _UL ⁽ⁱ⁾ ,
As coefficients d ⁽¹⁾ , d ⁽²⁾ , d ⁽³⁾ ,... And d ^(N) ,
d ⁽¹⁾ = 1,
_{^{d (2) = (f D}} L (1) / f U L (1)) / (f D L (2) / f U L (2)),
_{^{d (3) = (f D}} L (2) / f U L (2)) / (f D L (3) / f U L (3)),
…and
_{^{d (N) = (f D}} L (N-1) / f U L (N-1)) / (f D L (N) / f U L (N))
And the calibration coefficients c ⁽¹⁾ , c ⁽²⁾ , c ⁽³⁾ ,... And c ^(N) ,
c ⁽¹⁾ = d ⁽¹⁾
c ⁽²⁾ = d ⁽²⁾ × d ⁽¹⁾ ,
c ⁽³⁾ = d ⁽³⁾ × d ⁽²⁾ × d ⁽¹⁾ ,
... and c ^(N) = d ^(N) x d ^(N-1) x ... x d ⁽¹⁾
The calibration method of the radio | wireless communications system of Additional remark 11 or 12 which computes.

Claims (7)

A base station connected to a plurality of transmission / reception points,
A base station comprising a calibrator that calculates a calibration coefficient for correcting a weight in the beamforming communication of each of the plurality of transmission / reception points based on the beamforming communication of each of the plurality of transmission / reception points.   The base station according to claim 1, wherein the beamforming communication of each of the plurality of transmission / reception points is time division multiplex communication. The beam forming communication of each of the plurality of transmission / reception points is communication between a wireless device located in the base station and the plurality of transmission / reception points,
The calibrator calculates the calibration coefficient based on downlink radio characteristics from each of the plurality of transmission / reception points to the radio apparatus and uplink radio characteristics from the radio apparatus to each of the plurality of transmission / reception points. Or the base station of 2. Wherein the plurality of the number of transmitting and receiving points is N, the downstream radio characteristics from each of the plurality of transmission and reception points to the wireless device _{^{f DL (1), f DL}} (2), f DL (3), ... and _{f DL} ^{( N),} and the uplink radio characteristics from the wireless device to each of the plurality of transmission / reception points are f _UL ⁽¹⁾ , f _UL ⁽²⁾ , f _UL ⁽³⁾ ,... And f _UL ^(N) ,
The calibrators, the calibration factor ^{c _(1),} as ^{c (2), c (3} ), ... and ^{c (N),}
c ⁽¹⁾ = 1,
c ⁽²⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ),
c ⁽³⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽³⁾ / _fDL ⁽³⁾ ),
... and c ^(N) = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ^(N) / _fDL ^(N) )
The base station according to claim 3, wherein the base station is calculated. Wherein the plurality of the transmitting and receiving points ^{RRH (1), RRH (2} ), RRH (3), ... and the ^{RRH (N),} the beam forming communication by the plurality of receiving points, ^{RRH (1)} and RRH ^{(2 )} , RRH ⁽²⁾ and RRH ⁽³⁾ ,..., RRH ^(N−1) and RRH ^(N), respectively, and the radio characteristics from RRH ^{(i )} to RRH ^{(i + 1) are} expressed as f _DL ^{( i)} and the radio characteristics from RRH ^{(i + 1)} to RRH ⁽ⁱ⁾ are f _UL ⁽ⁱ⁾ ,
The calibrator uses coefficients c ⁽¹⁾ _, c ⁽²⁾ , c ⁽³⁾ ,... And c ^(N) as
c ⁽¹⁾ = 1,
c ⁽²⁾ = ( _fUL ⁽¹⁾ / _fDL ⁽¹⁾ ) / ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ),
c ⁽³⁾ = ( _fUL ⁽²⁾ / _fDL ⁽²⁾ ) / ( _fUL ⁽³⁾ / _fDL ⁽³⁾ ),
... and c ^(N) = ( _fUL ^(N-1) / _fDL ^(N-1) ) / ( _fUL ^(N) / _fDL ^(N) )
And the calibration coefficient is
c ⁽¹⁾ ,
c ⁽²⁾ xc ⁽¹⁾ ,
c ⁽³⁾ xc ⁽²⁾ xc ⁽¹⁾ ,
... and c ^(N) xc ^(N-1) x ... xc ⁽¹⁾
The base station according to claim 1, wherein the base station is calculated. A wireless communication system comprising a plurality of transmission / reception points and a base station connected to the plurality of transmission / reception points,
A wireless communication system including a calibrator that calculates a calibration coefficient for correcting a weight in the beam forming communication of each of the plurality of transmission / reception points based on the beam forming communication of each of the plurality of transmission / reception points. A calibration method of a wireless communication system comprising a base station connected to a plurality of transmission / reception points,
Beam forming communication is performed from each of the plurality of transmission / reception points,
A calibration method for a wireless communication system, wherein a calibration coefficient for correcting a weight in the beamforming communication at each of the plurality of transmission / reception points is calculated based on beamforming communication at each of the plurality of transmission / reception points.

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